NEW ORLEANS — Scientists in Michigan and Louisiana are predicting a big summer "dead zone" in the Gulf of Mexico unless a tropical storm hits the area shortly before or during the annual measurement. In the Chesapeake Bay, scientists expect a smaller-than-average area where there's too little oxygen to support fish, shellfish and other aquatic life.

The hypoxic zone in the Gulf is likely to be the largest since annual measurements began in 1985, covering 8,561 square miles — about the size of New Jersey, according to scientists from Louisiana State University and the Louisiana Universities Marine Consortium.

University of Michigan scientists predict that it will be smaller but still sizeable: the seventh-largest ever, at 7,286 square miles. That would be about the area of Connecticut, Rhode Island and the District of Columbia combined, according to the National Oceanic and Atmospheric Administration, which released those estimates and the one for the Chesapeake Bay on Tuesday.

Low- and no-oxygen areas in the Chesapeake Bay, the nation's largest estuary, aren't measured in square miles because so much of the bay is shallow. Instead, they're measured in cubic miles and water volume. This year's low-oxygen zone is expected to affect 1.46 cubic miles in midsummer, with no measurable oxygen in 0.26 to 0.38 cubic miles, according to researchers at the University of Michigan and the University of Maryland Center for Environmental Science. That is smaller than average, NOAA researchers said in news release.

The Gulf dead zone affects nationally important commercial and recreational fisheries and threatens the region's economy, according to NOAA. It said the Chesapeake dead zones, which have been highly variable in recent years, threaten a multi-year effort to restore the Bay's water quality and enhance its production of crabs, oysters and other important fisheries.

"Coastal hypoxia is proliferating around the world," said Donald Boesch, president of the University of Maryland Center for Environmental Science. "It is important that we have excellent abilities to predict and control the largest dead zones in the United States. The whole world is watching."

All the forecasts are based on nutrient runoff and river stream data from the U.S. Geological Survey. The nutrients are largely nitrogen and phosphorus, much of them from farms upriver.

Since 1995, the Gulf dead zone has averaged 5,960 square miles, an area roughly the size of Connecticut. In 2001 and 2008, state, federal and tribal agencies in the Mississippi River watershed — about 40 percent of the country — set a goal to reduce the size of the Gulf hypoxic zone to an average of 1,950 square miles by 2015.

There has been little progress getting there, said Donald Scavia, a University of Michigan aquatic ecologist who contributes to both forecasts.

"The size of the Gulf dead zone goes up and down depending on that particular year's weather patterns. But the bottom line is that we will never reach the action plan's goal of 1,950 square miles until more serious actions are taken to reduce the loss of Midwest fertilizers to the Mississippi River system, regardless of the weather," Scavia said.

Last year, drought upriver cut runoff so drastically that the Gulf of Mexico dead zone was the fourth-smallest on record, less than 2,900 square miles. Michigan scientists had predicted it would cover just under 1,200 square miles while Louisiana, scientists predicted about 6,200 square miles.

Aiming to jolt the rest of the world to action, President Barack Obama moved ahead Sunday with even tougher greenhouse gas cuts on American power plants, setting up a certain confrontation in the courts with energy producers and Republican-led states.